Erasers are not nearly as important today as they might have been in the past. Today, the speed of communication is the most important factor. Erasing just takes too much time. Whether one has a traditional eraser or an older form of an eraser such as bread, one should realize that crossing things out is so much faster.
Yes, I would be willing to go back to using bread or un-cured rubber blocks to erase my work because we all have to make sacrifices if the time comes. We need to preserve all of our resources and if something is running out, we must find different ways of getting the job done.
The use of bread or un-cured rubber blocks would not be a great burden to save a valuable resource. Bread would have the problem of mold or deterioration after carrying in a backpack or similar bag for school or work, but a block of un-cured rubber would be relatively easy to keep with you and the problem of mold and deterioration over time even without use would not be a problem. I may take time to become used to the scent and texture of using un-cured rubber but it would not be overly difficult.
If erasers were at risk of running low then it would be far more sensible to simply cross mistakes out or to start again rather than using other alternatives. Materials such as uncured rubber and bread are likely to do damage to the paper and defeat the object of rubbing something out to neaten the work.